Infections due to group B streptococci are a serious cause of morbidity and mortality in newborn infants, patients with diabetes mellitus and other immunocompromised hosts. Despite the uniform sensitivity of strains of this group to a number of antibiotics, these organisms continue to represent a serious problem in clinical medicine. The objectives of this research are to characterize the cellular and humoral components of the host defense mechanism against these bacterial pathogens. Studies are being carried out to determine the effect of type specific antibodies and the classic and alternative complement pathway in the opsonization of the 5 types of group B streptococci. In addition, bacterial factors important in virulence are being investigated. Attempts are being made to correlate opsonic antibody with antibody detected by radioimmunoassay and mouse protection. Preliminary studies have indicated that protective antibody can be supplied to infected neonates and this has markedly altered mortality rates due to this disease. We are also evaluating neonatal and adult phagocyte function in response to group B challenge using in vitro techniques and in infected patients. Lastly, we are attempting to develop more rapid means of detecting group B streptococci using counterimmunoelectrophoresis, latex agglutination and staphylococcal coagglutination.